ARC FURNACE ASSISTED CARBOTHERMAL
DECOMPOSITION OF ZIRCON
V. A. Sokolov
Translated from Novye Ogneupory, No. 4, pp. 78 – 81, April, 2005.
Original article submitted January 21, 2005.
Results of a thermodynamic analysis of the reduction of silicon from zircon are presented and a method for
carbothermal desiliconization of zircon using arc furnace technology are proposed. Fused materials with a re
sidual silicon concentration of 10 – 17% are prepared that can be used in the manufacture of fusion-cast
and zirconium dioxide (zirconia) ZrO
major components of the fusion-cast baddeleyite-corundum
refractories that are prepared by electric melting technology
in arc furnaces. In zircon, the mass ratio ZrO
therefore to maintain a ratio ZrO
of 2.8 – 3.2 as re-
quired for BK-37 and BK-41-grade refractories , zirconia
(material rather expensive) is added to the fusion mixture.
To make the manufacture of fusion-cast baddeleyite-co-
rundum refractories less expensive, methods were sought to
prepare partially desiliconized zircon. Thus, using a fluoride
decomposition method by the reaction
) + 4AlF
with the properly varied zircon to aluminum fluoride ratio,
one can remove an amount of silica to a fusion mixture in
conformance with requirements placed on industrial badde
leyite-corundum refractories .
A technology for production of ZrO
containing 3 – 5%
suited for baddeleyite-corundum refractories and abra
sives has been developed at the Giredmet (State Research
and Design Institute for Rare Metal Industry, Moscow, Rus
sia); it is based on the chalk-assisted decomposition of zircon
followed by leaching the bake produced with hydrochloric
acid . The TsrO-B-grade zirconia produced by this tech
nology and commercially available from the Verkhne-
Dneprovskii Mining and Smelting Plant (Ukraine) has been
used extensively in the manufacture of baddeleyite-corun
dum refractories at the Shcherbinka Electrofused Refractory
These methods of desiliconization, however, imply a
narrow specialization and for this reason have not gained
Partial desiliconization of zircon can be effected by a
carbothermal method using an arc furnace for melting zir-
con-containing fusion mixtures [5, 6].
In , an analysis of the high-temperature conversion of
zircon and processes involved in the carbothermal reduction
of zircon and silica has been given. The state diagram for the
system is shown in Fig. 1 .
Zircon at high temperature develops instability and de
composes into solid dioxides of zirconium and silicon by the
At 1931 K, zircon decomposes into pure, solid-state di
oxides of zirconium and silicon. In the temperature range of
1931 – 1960 K, these components persist in equilibrium. At
1960 K (eutectic temperature), a melt (SiO
+ 4 – 5 wt.%
) evolves. With further increase in temperature (up to a
monoeutectic temperature of 2523 K), the melt, while in
equilibrium with pure solid zirconia, becomes enriched in it
up to 38 wt.% ZrO
(at a temperature slightly below 2523 K)
or to 59 wt.% ZrO
(at a temperature slightly above 2523 K).
As the temperature is raised, the melting of ZrO
to become completed entirely at 2670 K; compositionally,
the liquid phase corresponds to the zircon stoichiometry
(67 wt.% ZrO
and 33 wt.% SiO
The temperature range of 1960 – 2670 K is suited for re
from the melt via partial or complete reduction
to obtain a fused product enriched in ZrO
Refractories and Industrial Ceramics Vol. 46, No. 3, 2005
1083-4877/05/4603-0208 © 2005 Springer Science+Business Media, Inc.
Moscow Institute for Steel and Alloys, Moscow, Russia.